1. Field of the Invention
The present invention generally relates to multiple output wavelength solid state lasers and more specifically, to a method and apparatus for exciting a multiple output wavelength solid state material to effect multiple nonoverlapping transitions providing simultaneous lasing at multiple transitions.
2. Description of Prior Art
Various types of lasers are known, which are classified according to their pumping or excitation scheme. The function of the pumping system is to maintain more atoms in the upper than the lower state, thereby assuring that stimulated emission, called gain will exceed absorption and losses. The wavelength at which the laser emits is dependent upon the particulars of the electronic transitions within the laser gain material. The particular emission wavelength is dependent on many factors including the amplifying medium, pump wavelength, and laser cavity mirrors. A desirable type of laser utilizes a solid state material as the amplifying medium since it generally requires relatively low pump energy for laser action and overall construction is more rugged for field deployment.
More than one wavelength is often desired which would require using two separate lasers, which obviously requires duplication of power supplies, optics, etc. Multiple wavelength laser emission is a more efficient solution that has been sought in the prior art, but that has problems. While the prior art has reported using non-solid state dual wavelength lasers none have established a basis for a specific apparatus that is dedicated to the task of resolving the particular problems at hand.
Two lasing media in the same oscillator have been used to generate two simultaneous output wavelengths. An example is the 193 nm and 248 nm output from a mixture of ArF and KrF in an eximer laser where each material lases separately. Mixtures of dyes can generate multiple wavelength output in dye lasers. Emission from separate stripes or layers in semiconductor lasers has been demonstrated, as has emission from separate dopants in rare earth doped crystals, and separate color centers in alkali halide crystals. These parallel media concepts require the sharing of pump energy, and are therefore of reduced efficiency.
Examples of dual laser emission from a single active medium usually involve emission from parallel transitions or up conversion, but these techniques often exhibit gain competition as demonstrated in laser dyes. Techniques in which different subsets of the lasing medium are lased have been demonstrated using for example polarization or half mirror isolation, but again the gain is divided between the separate laser wavelengths.
There is also known in the prior art the use of a gas laser for dual wavelength laser emission as disclosed by Akimoto and Brown in Optics Letters, July 1985, pages 333-334. This laser uses a dual wavelength HeNe laser, emitting on two "cascade" transitions. In this device, lasing at one wavelength actually enhances the output at the second transition, by increasing the population inversion of that transition. The system is however a gas laser, not a solid state laser.
What is needed in this instance is a multiple wavelength solid state laser technique where no reduced operating efficiencies because of the separate wavelengths.